A new rapid expert consultation from a standing committee of the National Academies of Sciences, Engineering, and Medicine responds to a request from the White House Office of Science and Technology Policy (OSTP) concerning the duration of viral shedding by stage of infection, clinical signs and symptoms, and patient attributes; the levels and duration of antibody response and related resistance to illness; and optimal duration of isolation of cases.
Shedding of infectious virus from the respiratory tract of an infected patient tends to be highest early in disease, and it is not uncommon for viral shedding in respiratory secretions to occur two to three days prior to the appearance of symptoms. This is followed by a prolonged period of viral shedding, but the extent to which this represents infectious virus is uncertain, the rapid expert consultation says. In addition, the role of shedding from the gastrointestinal tract in transmission is unclear.
Antibody responses begin to appear over a period of days to weeks after infection. Further investigation is needed to understand the duration of protective immunity for the COVID-19 virus, the rapid expert consultation says. The duration of the antibody response and acquired immunity to reinfection will be critical to understanding how effective vaccination is likely to be, how long the antibodies provide protection against reinfection, and whether it is possible to achieve herd immunity against COVID-19.
The committee noted that it anticipates that additional studies based on cases coming out of the United States and Europe will provide further information on these critical topics, among others, such as the effect of various treatments on length of the shedding period and the role of specific antibodies to inform possible therapies.
A separate new rapid expert consultation focused on laboratory testing says that the two general classes of diagnostic tests — one to detect viral RNA and the other to detect human antibodies directed against the virus — each have benefits and weaknesses. Technologies to increase speed, sensitivity, and portability of tests and decrease costs are being developed. Antibody tests are also valuable markers for past infection in populations, and can help determine needed public health interventions. Both types of tests require proper validation and longitudinal studies of infected individuals before they can be properly interpreted, the rapid expert consultation says.
The National Academies’ Standing Committee on Emerging Infectious Diseases and 21st Century Health Threats, assembled in early March at the request of OSTP and the U.S. Department of Health and Human Services’ Office of the Assistant Secretary for Preparedness and Response in response to the COVID-19 outbreak, has been providing rapid expert consultations on several topics, such as social distancing, severe illness in young adults, and crisis standards of care.
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